Dust, cats, peanuts, cockroaches. An odd grouping, but one with a common thread: allergies — a major cause of illness in the United States. Up to 50 million Americans, including millions of kids, have some type of allergy. In fact, allergies account for the loss of an estimated 2 million schooldays per year.

About Allergies

An allergy is an overreaction of the immune system to a substance that's harmless to most people. But in someone with an allergy, the body's immune system treats the substance (called an allergen) as an invader and overreacts, causing symptoms that can range from annoying to serious or life threatening.

In an attempt to protect the body, the immune system of the allergic person produces antibodies called immunoglobulin E (IgE). Those antibodies then cause mast cells and basophils (allergy cells in the body) to release chemicals (including histamine) into the bloodstream to defend against the allergen "invader."

It's the release of these chemicals that causes allergic reactions, affecting a person's eyes, nose, throat, lungs, skin, or gastrointestinal tract as the body attempts to rid itself of the invading allergen. Future exposure to that same allergen will trigger this allergic response again. This means that every time the person eats that particular food or is exposed to that particular allergen, he or she will have an allergic reaction.

Allergies can be seasonal (happening only at certain times of the year, like when pollen counts are high) or can occur any time someone comes in contact with an allergen.

Who Gets Allergies?

The tendency to develop allergies is often hereditary, which means it can be passed down through your genes. However, just because you, your partner, or one of your children might have allergies doesn't mean that all of your kids will definitely get them, too. And someone usually doesn't inherit a particular allergy, just the likelihood of having allergies.

But a few kids have allergies even if no family member is allergic. And a child who is allergic to one substance is likely to be allergic to others.

Common Airborne Allergens

Some of the most common things people are allergic to are airborne (carried through the air):

Dust mites are one of the most common causes of allergies. These microscopic insects live all around us and feed on the millions of dead skin cells that fall off our bodies every day. Dust mites are the main allergic component of house dust, which is made up of many particles and can contain things such as fabric fibers and bacteria, as well as microscopic animal allergens. Dust mites are present year-round in most parts of the United States (although they're much less common at high altitudes) and live in bedding, upholstery, and carpets.

Pollen is another major cause of allergies (most people know pollen allergy as hay fever or rose fever). Trees, weeds, and grasses release these tiny particles into the air to fertilize other plants. Pollen allergies are seasonal, and the type of pollen someone is allergic to determines when symptoms will occur. For example, in the mid-Atlantic states, tree pollination begins in February and lasts through May, grass from May through June, and ragweed from August through October; so people with these allergies are likely to experience increased symptoms during those times.

Pollen counts measure how much pollen is in the air and can help people with allergies determine how bad their symptoms might be on any given day. Pollen counts are usually higher in the morning and on warm, dry, breezy days, and lowest when it's chilly and wet. Although not always exact, the local weather report's pollen count can be helpful when planning outside activities.

Molds, another common allergen, are fungi that thrive both indoors and outside in warm, moist environments. Outdoors, molds can be found in poor drainage areas, such as in piles of rotting leaves or compost piles. Indoors, molds thrive in dark, poorly ventilated places such as bathrooms and damp basements, and in clothes hampers or under kitchen sinks. A musty odor suggests mold growth. Although molds tend to be seasonal, many can grow year-round, especially those indoors.

Pet allergens from warm-blooded animals can cause problems for kids and parents alike. Pet dander (tiny flakes of shed skin, fur, or feathers) can lead to allergies. (Contrary to popular belief, dander that causes allergies is not related to the length of an animal's fur or hair, and there is no such thing as a non-allergenic dog or cat.) Animal saliva also can be an allergen, when a pet licks someone, or licks him or herself. When pets lick themselves, the saliva gets on their fur or feathers. As the saliva dries, protein particles become airborne and work their way into fabrics in the home. Cats are the worst offenders because they tend to lick themselves more than other animals as part of grooming. Pet urine also can cause allergies in the same way when it gets on airborne fur or skin, or when a pet urinates in a spot that doesn't get cleaned.

Cockroaches are also a major household allergen, especially in inner cities. Exposure to cockroach-infested buildings may be a major cause of the high rates of asthma in inner-city kids.

Common Food Allergens

The American Academy of Allergy, Asthma, and Immunology estimates that up to 2 million, or 8%, of kids in the United States are affected by food allergies, and that eight foods account for most of those: cow's milk, eggs, fish, shellfish, peanuts, tree nuts, soy, and wheat.

Cow's milk(or cow's milk protein). Between 2% and 3% of infants are allergic to the proteins found in cow's milk and cow's milk-based formulas. Most formulas on the market are cow's milk-based. Cow's milk protein allergy means that someone has an abnormal immune system reaction to proteins found in the cow's milk used to make standard baby formulas, cheeses, and other milk products. Milk proteins also can be a hidden ingredient in many prepared foods. Many kids outgrow milk allergies.

Eggs. One of the most common food allergies in infants and young children, egg allergy can pose many challenges for parents. Eggs are used in many of the foods kids eat — and in many cases they're "hidden" ingredients. Kids tend to outgrow egg allergies as they get older.

Fish and shellfish. Fish and shellfish allergies are some of the more common adult food allergies and ones that people usually don't outgrow. Fish and shellfish are from different families of food, so having an allergy to one does not necessarily mean someone will be allergic to the other.

Peanuts and tree nuts. Peanut allergy is another common food allergy in kids, with the number of those who are allergic on the rise. (Peanuts are not a true nut, but a legume — in the same family as peas and lentils, although most people with peanut allergy don't have allergies to other legumes.) Another common allergy is to tree nuts, such as almonds, walnuts, pecans, hazelnuts, and cashews. Most people do not outgrow peanut or tree nut allergies.

Soy. Like peanuts, soybeans are legumes. Soy allergy is more common among babies than older children. Many infants who are allergic to cow's milk are also allergic to the protein in soy formulas. Soy proteins are often a hidden ingredient in prepared foods.

Wheat. Wheat proteins are found in many foods, and some are more obvious than others. Although wheat allergy is often confused with celiac disease, there is a difference. Celiac disease is caused by a sensitivity to gluten, which is found in wheat, rye, and barley. It can cause someone to feel ill and lead to damage in the small intestine. An allergy to wheat not only can make someone feel ill, but, just like other food allergies, it also can cause a life-threatening reaction.

Other Common Allergens

Insect stings. For most kids, being stung by an insect means swelling, redness, and itching at the site of the bite. But for those with insect venom allergy, an insect sting can cause more severe symptoms.

Medicines. Antibiotics (used to treat infections) are the most common types of medicines that cause allergic reactions. Many other medicines, prescription and over-the-counter, also can cause allergic reactions. If your child reacts to a medicine, talk to your doctor before assuming the reaction is a sign of allergy.

Chemicals. Sometimes, cosmetics or laundry detergents can cause an itchy rash. Usually, this is because someone has a reaction to the chemicals in these products. Dyes, household cleaners, and pesticides used on lawns or plants also can cause allergic reactions in some people.

Some kids also have what are called cross-reactions. For example, kids who are allergic to birch pollen might have symptoms when they eat an apple because that apple is made up of a protein similar to one in the pollen. Or kids who are allergic to latex (found in latex gloves or certain types of hospital equipment) are more likely to be allergic to foods like kiwifruit, water chestnuts, avocados, or bananas.

Signs and Symptoms

The type and severity of allergy symptoms vary from allergy to allergy and child to child. Allergies may show up as itchy eyes or an itchy nose, sneezing, nasal congestion, throat tightness, trouble breathing, vomiting, and even faintness or passing out. Severe allergic reactions (called anaphylaxis) can be fatal if not treated in time.

Airborne Allergy Symptoms

Airborne allergens can cause something known as allergic rhinitis, which occurs in about 7% to 10% of Americans. It usually develops by 10 years of age and reaches its peak in the teens or early twenties, with symptoms often disappearing between the ages of 40 and 60.

Symptoms can include:

sneezing

itchy nose and/or throat

nasal congestion

coughing

These symptoms are often accompanied by itchy, watery, and/or red eyes, which is called allergic conjunctivitis. (When dark circles are present around the eyes, they're called allergic "shiners.") Those who react to airborne allergens usually have allergic rhinitis and/or allergic conjunctivitis. Those who have asthma may have wheezing and shortness of breath from airborne allergens.

Symptoms of Food, Medicines, or Insect Venom Allergies

a drop in blood pressure, causing lightheadedness or loss of consciousness

Allergic reactions can differ. Sometimes the same person can react differently at different times. Some reactions are mild and involve only one system of the body, like hives on the skin. Other times the reaction can be more severe and involve more than one part of the body. A mild reaction in the past does not mean that a future reaction will also be mild.

About Anaphylaxis

Kids with severe allergies (such as those to food, medication, or insect venom) can be at risk for a sudden, potentially life-threatening allergic reaction called anaphylaxis. This reaction can be frightening — a child might faint or feel like his or her throat is closing, for example. But when treated properly, anaphylaxis can be managed.

Anaphylaxis isn't common, but if your child has allergies, it's important to know about it and be prepared. Anaphylaxis can begin with some of the same symptoms as a less severe reaction, but then can involve more than one part of the body. Reactions can quickly worsen, leading someone to have trouble breathing, swelling in the mouth or throat, dizziness, or fainting. If it is not treated, anaphylaxis can be fatal.

If your child has been diagnosed with a life-threatening allergy, the doctor will want him or her to carry an epinephrine auto-injector in case of an emergency. Epinephrine is a drug injection that enters the bloodstream and works quickly against serious allergy symptoms; for example, it decreases swelling and raises blood pressure. Kids with severe symptoms or reactions to an allergen require an injection of epinephrine and acall to 911 forimmediate medical attention.

Anaphylaxis can happen just seconds after being exposed to a triggering substance or can be delayed for up to 2 hours if the reaction is from a food. It can involve various areas of the body.

Fortunately, severe or life-threatening allergies occur in only a small group of kids. In fact, the annual incidence of anaphylactic reactions is only a tiny percentage of overall allergic reactions. Those with asthma or a history of a previous anaphylactic reaction are at greater risk for these severe reactions.

Diagnosing Allergies

Some allergies are fairly easy to identify because the pattern of symptoms following exposure to certain allergens can be hard to miss. But other allergies are less obvious because they can be similar to other conditions.

If your child has cold-like symptoms lasting longer than a week or two or develops a "cold" at the same time every year, consult your doctor, who will likely ask questions about the symptoms and when they appear. Based on the answers and a physical exam, the doctor might be able to make a diagnosis and prescribe medicines, or may refer you to an allergist for allergy tests and more extensive therapy.

To find the cause of an allergy, allergists usually do skin tests for the most common environmental and food allergens. A skin test can work in one of two ways:

A drop of a purified liquid form of the allergen is dropped onto the skin and the area is pricked with a small pricking device.

A small amount of allergen is injected just under the skin. This test stings a little but isn't extremely painful.

After about 15 minutes, if a lump surrounded by a reddish area appears (like a mosquito bite) at the injection site, the test is positive.

As an alternative test, blood tests may be used in children with skin conditions, those who are on certain medicines, or those who are extremely sensitive to a particular allergen.

Even if a skin test and/or a blood test shows an allergy, a child must also have symptoms to be diagnosed with an allergy. For example, a toddler who has a positive test for dust mites and sneezes a lot while playing on the floor would be considered allergic to dust mites.

Treating Allergies

There is no real cure for allergies, but it is possible to relieve symptoms. The only real way to cope with them is to reduce or eliminate exposure to allergens. That means that parents must educate their kids early and often, not only about the allergy itself, but also about the reactions they can have if they consume or come into contact with the allergen.

Informing any and all caregivers (childcare personnel, teachers, extended family members, parents of your child's friends, etc.) about your child's allergy is also important.

If reducing exposure to environmental allergens isn't possible or is ineffective, medicines may be prescribed, including antihistamines (which you can also buy over the counter), eye drops, and nasal sprays.

In some cases, an allergist may recommend immunotherapy (allergy shots) to help desensitize someone with an allergy. However, allergy shots are only helpful for allergens such as dust, mold, pollens, animals, and insect stings. They're not used for food allergies.

Don't hang heavy drapes and get rid of other items that allow dust to build up.

Clean when your child is not in the room.

Use special covers to seal pillows and mattresses if your child is allergic to dust mites.

For kids allergic to pollen, keep the windows closed when the pollen season is at its peak, change their clothing and bathe them after they've been outdoors, and don't let them mow the lawn.

Keep kids who are allergic to mold away from damp areas, such as some basements, and keep bathrooms and other mold-prone areas clean and dry.

Kids with food allergies need to completely avoid products made with their allergens. This can be tough as allergens can be found in many unexpected foods and products.

Always read labels to see if a packaged food contains your child's allergen. Manufacturers of foods sold in the United States must state in understandable language whether foods contain any of the top eight most common allergens. This label requirement makes things a little easier. But it's important to remember that "safe" foods could become unsafe if food companies change ingredients, processes, or production locations.

Cross-contamination means that the allergen is not one of the ingredients in a product, but might have contaminated it during production or packaging. Companies are not required to label for cross-contamination risk, though some voluntarily do so. You may see advisory statements such as "May contain...," "Processed in a facility that also processes...," or "Manufactured on equipment also used for ...."

Since products without precautionary statements also might be cross-contaminated and the company simply chose not to label for it, it is always best to contact the company to see if the product could contain your child's allergen. You might find this information on the company's website, or you can contact a company representative via email.

Cross-contamination also can happen at home or in restaurants when kitchen surfaces or utensils are used for different foods.

Injectable Epinephrine

If your child has been diagnosed with a life-threatening allergy, the doctor will want him or her to carry an epinephrine auto-injector in case of an emergency.

Available in an easy-to-carry container that is the size of a large marker or a smartphone, injectable epinephrine is carried by millions of parents (and older kids) everywhere they go. With an injection into the thigh, the device administers epinephrine to ease the allergic reaction.

An injectable epinephrine prescription usually includes two auto-injectors and a "trainer" that contains no needle or epinephrine, but allows you and your child (if old enough) to practice using the device. It's vital that you familiarize yourself with the procedure by practicing with the trainer. Your doctor also can provide instructions on how to use and store injectable epinephrine.

Make sure kids who are old enough to use it themselves keep injectable epinephrine readily available at all times. If your child is younger, talk to the school nurse, teachers, and your childcare provider about keeping injectable epinephrine on hand nearby in case of an emergency.

It's also important to ensure that injectable epinephrine devices are available in your home and in the homes of friends and family members if your child spends time there. Your doctor may also encourage your child to wear a medical alert bracelet. It's also wise to carry an over-the-counter antihistamine, which can help alleviate allergy symptoms in some people. But antihistamines should not be used as a replacement for the epinephrine pen.

Kids who have had to take injectable epinephrine should go immediately to a medical facility or hospital emergency department, where additional treatment can be given if needed. Up to 1 in 5 anaphylactic reactions can have a second wave of symptoms several hours following the initial attack, so these kids might need to be watched in a clinic or hospital for several hours after the reaction even though they seem well.

The good news is that only a very small group of kids will experience severe or life-threatening allergic reactions. With proper diagnosis, preventive measures, and treatment, most kids can keep their allergies in check and live happy, healthy lives.